Device and method for continuous screen printing of organic light emitting diodes

ABSTRACT

Devices and method for continuous printing of organic light-emitting diodes (OLEDs) are described. A substrate with or without coating is provided as strip material on a roll, and is fed through a device with movable screens for imprinting by screen printing.

BACKGROUND

The invention relates to a device and method for continuous printing oforganic light-emitting diodes (OLEDs).

Organic light-emitting diodes (OLEDs), based on organic material such aspolymers and/or “small molecules” as the principal material of thefunctional layers, have developed very rapidly in recent years. Improvedefficiency, a large number of new colors, and lower usage voltages makethem of interest for many areas of application. Typical applications canbe low-information-content passive-matrix displays with a few thousandpixels and an icon bar, backlights for LCDs, or planar illuminationelements. The advantages of OLEDs, such as Lambert's reradiation andminimal thickness, are useful for these applications.

At present, the functional layers of which an OLED consists (e.g.,poly(1,4-phenylene vinylene), PPV or polyfluorene, and/or derivatives ofthese materials) are usually applied to the glass or film substrateand/or to a bottom and/or structured layer using the spin-on applicationmethod. This method has a number of drawbacks: the bulk of the polymersolution (about 98%) is irretrievably lost, the spin-on applicationprocess is relatively lengthy (about 30-60 seconds) and, in the case oflarger substrates, it is almost impossible to apply homogeneousfunctional layers.

For these reasons, alternative methods of applying organic material ontolarge surfaces are being sought. A number of printing processes aresuitable for this purpose: screen printing, pad printing, inkjetprinting, letterpress and rotogravure methods [e.g., D. A. Pardo, G. E.Jabbour, and N. Peyghambrian, “Application of Screen Printing in theFabrication of Organic Light-Emitting Devices”; Adv. Mat., 2000, 17, p.1249-1252; K. Mori et al., “Organic Light-Emitting Devices Patterned byScreen-Printing”; Jpn. J. Appl. Phys., 2000, 39, p. 942-944; Birnstocket al., “Screen-printed passive matrix displays based on light-emittingpolymers”; Appl. Phys. Lett., Vol. 78, No. 24, 2001]. These printingmethods are also advantageous because they permit the organic materialto be applied after it has already been structured, making multichromeor full-color OLEDs possible.

Where a majority of the processes have thus far been developed for glasssubstrates, flexible substrates (e.g., films) will become increasinglyimportant in the future.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE shows a schematic of a continuous screen printing system.

The goal of the invention is to provide a device and method for thecontinuous application of soluble organic material, especially polymers,to substrate, especially flexible substrates, which operatecontinuously.

For economic reasons, the substrates should no longer be printed using a“stop-and-go” method, as is the case with classic printing on glasssubstrate, but instead should be coated in a continuous process usingstrip material, such as material “on a roll.” In this process, the filmsubstrate 10, which maybe pre-structured, is supplied on a roll 20 andis imprinted with one or more polymers as the film 10 is unwound fromthe roll 20 in a uniform motion.

The invention solves the problem in that a special screen printingmethod is used to print the OLEDs.

The subject matter of the invention is a device 100 for the continuousimprinting of a substrate-strip material 10 by means of screen printing,comprising at least one printing screen 5 and in which the substratestrip material 10 is supplied on a roll 20, wherein a device 30 formoving the printing screen 5 is provided which ensures that it canaccompany the strip material 10 during printing and, following printing,be returned to its original position.

Another subject matter of the invention is a method for imprinting asubstrate strip material 10 by means of screen printing, in which thesubstrate is moved past at least one screen 5, wherein the screen 5accompanies the strip material 10 during printing.

Finally, a subject matter of the invention is a product such as an OLED,which comprises at least one functional layer 40 that was applied in acontinuous process by means of screen printing.

DETAILED DESCRIPTION

The term substrate strip material preferably describes flexiblesubstrates such as films, etc., which exist in strip form. The substrateserves as the carrier of an OLED.

According to an advantageous embodiment, the device comprises a row ofidentically acting screens that are arranged in series and accompanysuccessive areas of the strip material during printing. In particular,the row of screens consisting of an organic material and/or a screenstencil is arranged in such a way that there are no non-printed andtherefore unusable areas on the strip material. Thus, virtually 100% ofthe strip is utilized and a section of the completely coated stripproduces two edges of two substrates.

According to an embodiment, the device prints at a level of precisionthat typically permits a tolerance of only a few dozen μm.

According to an embodiment of the method, the substrate strip materialis imprinted at a typical speed of 0.5 m/s, preferably in the range of0.25 to 1 m/s.

Strip widths are preferably between 50 and 500 mm, depending on theapplication.

According to an advantageous embodiment of the device, severaldifferently operating screens or rows of screens are arranged in series,so that a complete OLED can be produced in one device.

A substrate strip material is typically 0.005 to 1 mm thick and 50 to500 mm wide.

It can also be advantageous that a certain distance between oneimprinted area and the next on the substrate strip material is desired,so that a device without rows of screens, which has only one screen foreach printing sub-step, is certainly preferable to a device with rows ofscreens, i.e., several identically operating screens for each printingsub-step. It can also be provided that, in a device with severalscreens, a row of screens can be used variably or parked, meaning thatthey are used or not used, depending on requirements. In addition to thescreens with the template, a wiper blade 25 and a tank for the solutionof organic material, the device can also comprise a device forirradiating 45 UV-curable functional layers, a heating system, a blower,a distributor and/or another apparatus for producing an OLED.

In one embodiment, a chatting 60 and/or stamping device 50 forseparating and/or encapsulating the individual OLEDs 110 is provided atthe output of the device, where the fully printed strip material exitsthe device.

Other elements, such as the device for unwinding the substrate-stripmaterial as well as for maintaining the necessary strip tension areaalso comprised by the device and are part of the state of the art, whichis the reason they are not described in great detail.

The imprinting of a uniformly moving film is not trivial, because theclassic “roll-on-roll” processes (offset printing, etc.) cannot be used.This is because the photosensitive resist structures already located onthe film are critical in this regard. As a result of these contactmethods, they are either destroyed or transfer of the polymer solutionis prevented. The conventional “stop and go” procedure unnecessarilystresses the substrate film during printing, which is not the case withthe continuous method.

Another advantage of the process is the high speed and great precisionwith which the OLEDs can be produced.

In the following, the invention is described in greater detail on thebasis of an exemplary embodiment:

The production of a flexible, monochromatic display based on organiclight-emitting diodes using the special “screen-on-roll” screen printingmethod:

A transparent film 10 impermeable to water and oxygen is structured withITO 15 (indium tin oxide) and provided with photoresist structures. (Thepurpose of the photosensitive resist structures is to separate theindividual cathode strips and confine the printed polymer surfaces.These processes are known and well-understood.) As a result of thepre-structuring of the film, hundreds of individual passive-matrixdisplays are defined. The film is provided wrapped on a roll 20. Usingthe special screen printing machine 100, several conjugated polymers areconsecutively printed onto the film and dried using suitable means. Inthis printing process, the film can be moved through the machine in auniform motion. Finally, a cathode 70 is vapor deposited using a vapordeposition device 80 in a structured manner (e.g., through shadow masks35) and the active side of the film is also sealed to be watertight andairtight. Now the individual displays can be cut out using a cuttingdevice 60 and contacted.

The invention relates to a device and method for continuous printing oforganic light-emitting diodes 110 (OLEDs). In this connection, asubstrate with or without coating is provided as strip material 10 on aroll 20, and is fed through a device with movable screens for imprintingby means of screen printing.

1. A device for continuous imprinting of a substrate strip material thatis supplied on a roll to form organic light emitting devices on thesubstrate strip material, comprising: a first printing screen; aprinting screen moving device to cause the first printing screen to movewith the substrate strip material from a first position, the firstprinting screen configured to accompany the substrate strip material asthe substrate strip material is unwound from the roll, and to return tothe first position, the device configured to form UV-curable organicfunctional layers on the substrate strip; a UV irradiating device forirradiating the UV-curable organic functional layers; and anencapsulation device for encapsulating individual organic light emittingdiodes that are formed on the substrate strip material.
 2. The device ofclaim 1, further comprising: a row of printing screens including thefirst printing screen.
 3. The device of claim 2, wherein: the printingscreens in the row of printing screens operate identically.
 4. thedevice of claim 2, wherein: at least two printing screens in the row ofprinting screens operate differently from each other.
 5. The device ofclaim 1, wherein: the first printing screen includes an organicmaterial.
 6. The device of claim 1, further comprising: a secondprinting screen positioned in series with the first printing screen. 7.The device of claim 1, further comprising at least one of a heatingsystem, a blower or a distributor.
 8. The device of claim 1, furthercomprising: a cutting device for separating the substrate strip materialinto individual organic light emitting diodes.
 9. The device of claim 1,wherein: the printing screen moving device moves the printing screen ata speed of about 0.25 m/s to about 1 m/s.
 10. The device of claim 1,wherein: the printing screen moving device moves the printing screen ata speed of about 0.5 m/s.
 11. The device of claim 1, further comprising:a wiper blade for forcing organic material through the first printingscreen; and a tank for providing a solution of the organic material. 12.A method for continuous imprinting of a substrate strip material that issupplied on a roll to form organic light emitting devices on thesubstrate strip material, comprising: moving the substrate stripmaterial from a roll through a device having a printing screen; movingthe printing screen with the substrate strip material; printing onto thesubstrate strip material using the printing screen as the screen moveswith the substrate strip material and as the substrate strip material isunwound from the roll, forming UV-curable organic functional layers onthe substrate strip; curing the UV-curable organic functional layerswith UV light; and encapsulating individual organic light emittingdiodes formed on the substrate strip material.
 13. The method of claim12, wherein: moving the printing screen includes moving the screenbetween a speed of about 0.25 m/s to about 1 m/s.
 14. The method ofclaim 12, wherein: moving the printing screen includes moving the screenat a speed of about 0.5 m/s.
 15. The method of claim 12, furthercomprising: cutting a printed substrate strip material to separateindividual organic light emitting diodes.
 16. A method for continuousimprinting of a substrate strip material that is supplied on a roll toform organic light emitting devices on the substrate strip material,comprising: unwinding a substrate from a roll through a device having aplurality of printing screens; printing a conjugated polymer onto thesubstrate using the plurality of printing screens as the substrate movesthrough the device to form a printed substrate strip; moving theprinting screens with the substrate; depositing a cathode onto theprinted substrate strip; encapsulating the printed substrate strip toencapsulate individual organic light emitting diodes; and cutting theprinted substrate strip to separate the individual organic lightemitting diodes.